title: Conservation of surfactant protein A: evidence for a single origin for vertebrate pulmonary surfactant.
abstract: Surface tension is reduced at the air-liquid interface in the lung by a mixture of lipids and proteins termed pulmonary surfactant. This study is the first to provide evidence for the presence of a surfactant-specific protein (Surfactant Protein A-SP-A) in the gas-holding structures of representatives of all the major vertebrate groups. Western blot analysis demonstrated cross-reactivity between an antihuman SP-A antibody and material lavaged from lungs or swimbladders of members from all vertebrate groups. Immunocytochemistry localized this SP-A-like protein to the air spaces of lungs from the actinopterygiian fish and lungfish. Northern blot analysis indicated that regions of the mouse SP-A cDNA sequence are complementary to lung mRNA from all species examined. The presence of an SP-A-like protein and SP-A mRNA in members of all the major vertebrate groups implies that the surfactant system had a single evolutionary origin in the vertebrates. Moreover, the evolution of the surfactant system must have been a prerequisite for the evolution of airbreathing. The presence of SP-A in the goldfish swimbladder demonstrates a role for the surfactant system in an organ that is no longer used for airbreathing.
authors.affiliation: Department of Physiology, University of Adelaide, Adelaide SA 5005, Australia.
authors.forename: L C
authors.initials: LC
authors.lastname: Sullivan
authors.forename: C B
authors.initials: CB
authors.lastname: Daniels
authors.forename: I D
authors.initials: ID
authors.lastname: Phillips
authors.forename: S
authors.initials: S
authors.lastname: Orgeig
authors.forename: J A
authors.initials: JA
authors.lastname: Whitsett
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D019143:Evolution, Molecular; D006801:Humans; D007150:Immunohistochemistry; D008168:Lung / Q000378:metabolism*; D011510:Proteolipids / Q000502:physiology*; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000502:physiology*; D014714:Vertebrates
chemical_list: D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants